The invention relates to an apparatus for making noncontacting measurements of electric fields which extend into the GHz range and or are statical by utilizing the Pockels effect in optically active crystals, with the crystal serving as a sensor and being subjected to the influence of the electric field.
In industrial technology and research there often exists the problem of measuring voltage under greatly limited measuring conditions, such as:
(1) the separation of potentials, i.e. it is not possible to measure voltage from either the ground end or the other end of a sensor lead line;
(2) interference-free transmission of the measurement signal even through stray electromagnetic fields, and also specifically through high-frequency interfering fields;
(3) measurements under difficult environmental conditions, e.g. high temperatures, explosion endangered rooms (where it is necessary to avoid spark development), or chemically active liquids;
(4) the measuring probe must be of ultrasmall dimensions so as to avoid excessively influencing the field to be measured;
(5) the measuring sensors must be composed of a dielectric medium which is an insulator, to avoid use of metal since metal interferes with the given field distribution (which would thereby cause the measured value to be inaccurate), whereas an insulator itself does not carry current and therefore reduces the danger of an electric spark-over to the measuring probe; and
(6) The capability for measurement throughout a wide frequency bandwidth, particularly in connection with high-frequency fields.
Generally, known measuring methods employ metal sensors for this purpose, such as a Rogowski coil or a capacitive voltage divider. Such measuring methods have considerable drawbacks. In such known measuring methods, feasible measurements have a bandwidth only in a range from 70 to 80 MHz with the consequence that the signals are accurate only to 12 to 14 nsec. Usually metal sensors cannot be employed where measurements would actually be of interest, namely in regions having high electric field intensities, such as, for example, in a pseudo spark chamber or other complex devices. Furthermore, with such known types of measuring devices, the measured signal value is often highly inaccurate with respect to the actual signal value, and high-frequency interference effects occur due to resonances with the metal sensors, oscillations of the sensors, and grounding problems.